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Chapter 14: Object-Oriented Data Modeling. Modern Database Management Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden. Objectives. Definition of terms Describe phases of object-oriented development life cycle State advantages of object-oriented modeling

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chapter 14 object oriented data modeling

Chapter 14: Object-Oriented Data Modeling

Modern Database Management

Jeffrey A. Hoffer, Mary B. Prescott,

Fred R. McFadden

objectives
Objectives
  • Definition of terms
  • Describe phases of object-oriented development life cycle
  • State advantages of object-oriented modeling
  • Compare object-oriented model with E-R and EER models
  • Model real-world application using UML class diagram
  • Provide UML snapshot of a system state
  • Recognize when to use generalization, aggregation, and composition
  • Specify types of business rules in a class diagram
what is object oriented data modeling
What is Object-Oriented Data Modeling?
  • Centers around objects and classes
  • Involves inheritance
  • Encapsulates both data and behavior
  • Benefits of Object-Oriented Modeling
    • Ability to tackle challenging problems
    • Improved communication between users, analysts, designer, and programmers
    • Increased consistency in analysis and design
    • Explicit representation of commonality among system components
    • System robustness
    • Reusability of analysis, design, and programming results
oo vs eer data modeling
OO vs. EER Data Modeling

EER

Object Oriented

Class

Entity type

Object

Entity instance

Association

Relationship

Inheritance of attributes

Inheritance of attributes

Inheritance of behavior

No representation of behavior

Object-oriented modeling is frequently accomplished using the Unified Modeling Language (UML)

classes and objects
Classes and Objects
  • Class: An entity that has a well-defined role in the application domain, as well as state, behavior, and identity
    • Tangible: person, place or thing
    • Concept or Event: department, performance, marriage, registration
    • Artifact of the Design Process: user interface, controller, scheduler
  • Object: a particular instance of a class

Objects exhibit BEHAVIOR as well as attributes

 Different from entities

state behavior identity
State, Behavior, Identity
  • State: attribute types and values
  • Behavior: how an object acts and reacts
    • Behavior is expressed through operations that can be performed on it
  • Identity: every object has a unique identity, even if all of its attribute values are the same
slide8

Figure 14-2 UML class and object diagram

a) Class diagram showing two classes

Class diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships.

slide9

Figure 14-2 UML class and object diagram (cont.)

b) Object diagram with two instances

Object diagram shows instances that are compatible with a given class diagram.

operations
Operations
  • A function or service that is provided by all instances of a class
  • Types of operations:
    • Constructor: creates a new instance of a class
    • Query: accesses the state of an object but does not alter its state
    • Update: alters the state of an object
    • Scope: operation applying to the class instead of an instance

Operations implement the object’s behavior

associations
Associations
  • Association:
    • Relationship among object classes
  • Association Role:
    • Role of an object in an association
    • The end of an association where it connects to a class
  • Multiplicity:
    • How many objects participate in an association. Lower-bound..Upper bound (cardinality)
slide12

Figure 14-3

Examples of association relationships of different degrees

Unary

Lower-bound – upper-bound

Represented as:

0..1, 0..*, 1..1, 1..*

Similar to minimum/maximum cardinality rules in EER

Binary

Ternary

slide13

Alternative multiplicity representation: specifying the two possible values in a list instead of a range

Figure 14-4 Examples of binary association relationships

a) University example

slide15

Figure 14-5

Object diagram for customer order example

association class
Association Class
  • An association that has attributes or operations of its own or that participates in relationships with other classes
  • Like an associative entity in ER model
slide17

Binary association class with behavior

Unary association with only attributes and no behavior

Figure 14-6 Association class and link object

a) Class diagram showing association classes

slide18

Association class

instances

Figure 14-6 Association class and link object (cont.)

b) Object diagram showing link objects

slide20

Figure 14-8 Derived attribute, association, and role

Constraint expression for derived attribute

Derived attribute

Derived relationship (from Registers-for and Scheduled-for)

Derived attributes and relationships shown with / in front of the name

generalization specialization
Generalization/Specialization
  • Subclass, superclass
    • similar to subtype/supertype in EER
  • Common attributes, relationships, AND operations
  • Disjoint vs. Overlapping
  • Complete (total specialization) vs. incomplete (partial specialization)
  • Abstract Class: no direct instances possible, but subclasses may have direct instances
  • Concrete Class: direct instances possible
slide22

An employee can only be one of these subclasses

Shared attributes and operations

An employee may be none of them.

Specialized attributes and operations

Figure 14-9 Examples of generalization, inheritance, and constraints

a) Employee superclass with three subclasses

slide23

A patient MUST be EXACTLY one of the subtypes

Dynamic means a

patient can change from one subclass to another over time

Figure 14-9 Examples of generalization, inheritance, and constraints (cont.)

b) Abstract Patient class with two concrete subclasses

Abstract indicated by italics

class scope attribute
Class-Scope Attribute
  • Specifies a value common to an entire class, rather than a specific value for an instance.
  • Represented by underlining
  • “=“ is initial, default value.
polymorphism
Polymorphism
  • Abstract Operation: Defines the form or protocol of the operation, but not its implementation
  • Method: The implementation of an operation
  • Polymorphism: The same operation may apply to two or more different classes in different ways
slide26

This operation is abstract…it has no method at Student level

Class-scope attributes–only one value common to all instances of these classes (includes default values)

Methods are defined at subclass level

Figure 14-11 Polymorphism, abstract operation, class-scope attribute, and ordering

overriding inheritance
Overriding Inheritance
  • Overriding: The process of replacing a method inherited from a superclass by a more specific implementation of that method in a subclass
    • For Extension: add code
    • For Restriction: limit the method
    • For Optimization: improve code by exploiting restrictions imposed by the subclass
slide28

Restrict job placement

Figure 14-12 Overriding inheritance

Subclasses that do not override place-student use the default behavior

multiple inheritance
Multiple Inheritance
  • Multiple Classification: An object is an instance of more than one class
  • Multiple Inheritance: A class inherits features from more than one superclass
aggregation
Aggregation
  • Aggregation: A part-of relationship between a component object and an aggregate object
  • Composition: A stronger form of aggregation in which a part object belongs to only one whole object and exists only as part of the whole object
  • Recursive Aggregation: Composition where component object is an instance of the same class as the aggregate object
slide32

Figure 14-14 Example of aggregation

A Personal Computer includes CPU, Hard Disk, Monitor, and Keyboard as parts. But, these parts can exist without being installed into a computer. The open diamond indicates aggregation, but not composition

slide33

Figure 14-15 Aggregation and Composition

(a) Class diagram

Closed diamond indicates composition. The room cannot exist without the building

(b) Object diagram

business rules
Business Rules
  • See Chapters 3 and 4
  • Implicit and explicit constraints on objects – for example:
    • cardinality constraints on association roles
    • ordering constraints on association roles
  • Business rules involving two graphical symbols:
    • labeled dashed arrow from one to the other
  • Business rules involving three or more graphical symbols:
    • note with dashed lines to each symbol
slide36

Three-symbol constraint

Two-symbol constraint

Figure 14-17 Representing business rules